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Add force_filter and compression_level parameters to (new) `stbi_write_png_to_mem_ex`

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* `force_filter` being < 0 means the original behavior (i.e. figure out
  the best-performing filter per scanline); any other values 0 <= x <= 4 correspond
  to PNG filters (0 = none, 1 = sub, 2 = up, 3 = average, 4 = Paeth).
* `compression_level` being < 0 equals `compression_level` 8 (the previous value).
  The higher this is, the better the compression should be (though it will use
  more memory).

These new parameters are not (yet) exposed for the higher-level API functions.
master
Aarni Koskela ago%!(EXTRA string=8 years)
parent 9d9f75eb68
commit 2c7b00ac21
1 changed files with 70 additions and 38 deletions
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  1. 108
      stb_image_write.h

108
stb_image_write.h
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@ -910,62 +910,90 @@ static unsigned char stbiw__paeth(int a, int b, int c)
return STBIW_UCHAR(c);
}
// @OPTIMIZE: provide an option that always forces left-predict or paeth predict
unsigned char *stbi_write_png_to_mem(unsigned char *pixels, int stride_bytes, int x, int y, int n, int *out_len)
static void stbiw__encode_png_line(unsigned char *pixels, int stride_bytes, int x, int y, int n, int filter_type, signed char *line_buffer) {
static int mapping[] = { 0,1,2,3,4 };
static int firstmap[] = { 0,1,0,5,6 };
int *mymap = (y != 0) ? mapping : firstmap;
int i;
int type = mymap[filter_type];
unsigned char *z = pixels + stride_bytes * y;
for (i = 0; i < n; ++i) {
switch (type) {
case 0: line_buffer[i] = z[i]; break;
case 1: line_buffer[i] = z[i]; break;
case 2: line_buffer[i] = z[i] - z[i-stride_bytes]; break;
case 3: line_buffer[i] = z[i] - (z[i-stride_bytes]>>1); break;
case 4: line_buffer[i] = (signed char) (z[i] - stbiw__paeth(0,z[i-stride_bytes],0)); break;
case 5: line_buffer[i] = z[i]; break;
case 6: line_buffer[i] = z[i]; break;
}
}
for (i=n; i < x*n; ++i) {
switch (type) {
case 0: line_buffer[i] = z[i]; break;
case 1: line_buffer[i] = z[i] - z[i-n]; break;
case 2: line_buffer[i] = z[i] - z[i-stride_bytes]; break;
case 3: line_buffer[i] = z[i] - ((z[i-n] + z[i-stride_bytes])>>1); break;
case 4: line_buffer[i] = z[i] - stbiw__paeth(z[i-n], z[i-stride_bytes], z[i-stride_bytes-n]); break;
case 5: line_buffer[i] = z[i] - (z[i-n]>>1); break;
case 6: line_buffer[i] = z[i] - stbiw__paeth(z[i-n], 0,0); break;
}
}
}
unsigned char *stbi_write_png_to_mem_ex(unsigned char *pixels, int stride_bytes, int x, int y, int n, int *out_len, int force_filter, int compression_level)
{
int ctype[5] = { -1, 0, 4, 2, 6 };
unsigned char sig[8] = { 137,80,78,71,13,10,26,10 };
unsigned char *out,*o, *filt, *zlib;
signed char *line_buffer;
int i,j,k,p,zlen;
int j,zlen;
if (stride_bytes == 0)
stride_bytes = x * n;
if (force_filter >= 5) {
force_filter = -1;
}
if (compression_level < 0) {
// TODO: What's the upper limit for compression_level?
compression_level = 8;
}
filt = (unsigned char *) STBIW_MALLOC((x*n+1) * y); if (!filt) return 0;
line_buffer = (signed char *) STBIW_MALLOC(x * n); if (!line_buffer) { STBIW_FREE(filt); return 0; }
for (j=0; j < y; ++j) {
static int mapping[] = { 0,1,2,3,4 };
static int firstmap[] = { 0,1,0,5,6 };
int *mymap = (j != 0) ? mapping : firstmap;
int best = 0, bestval = 0x7fffffff;
for (p=0; p < 2; ++p) {
for (k= p?best:0; k < 5; ++k) { // @TODO: clarity: rewrite this to go 0..5, and 'continue' the unwanted ones during 2nd pass
int type = mymap[k],est=0;
unsigned char *z = pixels + stride_bytes*j;
for (i=0; i < n; ++i)
switch (type) {
case 0: line_buffer[i] = z[i]; break;
case 1: line_buffer[i] = z[i]; break;
case 2: line_buffer[i] = z[i] - z[i-stride_bytes]; break;
case 3: line_buffer[i] = z[i] - (z[i-stride_bytes]>>1); break;
case 4: line_buffer[i] = (signed char) (z[i] - stbiw__paeth(0,z[i-stride_bytes],0)); break;
case 5: line_buffer[i] = z[i]; break;
case 6: line_buffer[i] = z[i]; break;
}
for (i=n; i < x*n; ++i) {
switch (type) {
case 0: line_buffer[i] = z[i]; break;
case 1: line_buffer[i] = z[i] - z[i-n]; break;
case 2: line_buffer[i] = z[i] - z[i-stride_bytes]; break;
case 3: line_buffer[i] = z[i] - ((z[i-n] + z[i-stride_bytes])>>1); break;
case 4: line_buffer[i] = z[i] - stbiw__paeth(z[i-n], z[i-stride_bytes], z[i-stride_bytes-n]); break;
case 5: line_buffer[i] = z[i] - (z[i-n]>>1); break;
case 6: line_buffer[i] = z[i] - stbiw__paeth(z[i-n], 0,0); break;
}
}
if (p) break;
for (i=0; i < x*n; ++i)
int filter_type;
if (force_filter > -1) {
filter_type = force_filter;
stbiw__encode_png_line(pixels, stride_bytes, x, j, n, force_filter, line_buffer);
} else { // Estimate the best filter by running through all of them:
int best_filter = 0, best_filter_val = 0x7fffffff, est, i;
for (filter_type = 0; filter_type < 5; filter_type++) {
stbiw__encode_png_line(pixels, stride_bytes, x, j, n, filter_type, line_buffer);
// Estimate the entropy of the line using this filter; the less, the better.
est = 0;
for (i = 0; i < x*n; ++i) {
est += abs((signed char) line_buffer[i]);
if (est < bestval) { bestval = est; best = k; }
}
if (est < best_filter_val) {
best_filter_val = est;
best_filter = filter_type;
}
}
if (filter_type != best_filter) { // If the last iteration already got us the best filter, don't redo it
stbiw__encode_png_line(pixels, stride_bytes, x, j, n, best_filter, line_buffer);
filter_type = best_filter;
}
}
// when we get here, best contains the filter type, and line_buffer contains the data
filt[j*(x*n+1)] = (unsigned char) best;
// when we get here, filter_type contains the filter type, and line_buffer contains the data
filt[j*(x*n+1)] = (unsigned char) filter_type;
STBIW_MEMMOVE(filt+j*(x*n+1)+1, line_buffer, x*n);
}
STBIW_FREE(line_buffer);
zlib = stbi_zlib_compress(filt, y*( x*n+1), &zlen, 8); // increase 8 to get smaller but use more memory
zlib = stbi_zlib_compress(filt, y*( x*n+1), &zlen, compression_level);
STBIW_FREE(filt);
if (!zlib) return 0;
@ -1003,6 +1031,10 @@ unsigned char *stbi_write_png_to_mem(unsigned char *pixels, int stride_bytes, in
return out;
}
unsigned char *stbi_write_png_to_mem(unsigned char *pixels, int stride_bytes, int x, int y, int n, int *out_len) {
return stbi_write_png_to_mem_ex(pixels, stride_bytes, x, y, n, out_len, -1, -1);
}
#ifndef STBI_WRITE_NO_STDIO
STBIWDEF int stbi_write_png(char const *filename, int x, int y, int comp, const void *data, int stride_bytes)
{

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